In an internal combustion engine, the valve train comprises a mechanical steel rocker arm located on the cylinder head, a push rod agitates in a up and downward motion of which seats in a valve lifter, driven by a camshaft. The push rod pushes on one end of the rocker arm, pivoting on a supported member located on the cylinder head, and in turn opens the engines valves when pushed upwardly. These units are fixed, a conventional system following the pattern of the camshaft. However, with high performance cams the valves are timed to have considerable overlap and duration in order to provide for a large fuel flow through the engine. At low speeds this large overlap is not necessary and the engine runs inefficiently, resulting in a loss in low speed horsepower. Basically, increasing the valve lash will shorten valve open duration and reduce overlap, increasing crankshaft rotating degrees in relationship to the opening of the valves. This results in an improvement in low speed performance. However, excessive lash causes considerable noise, wear and loss of horsepower at higher revolutions per minute.
The novel hydraulic rocker arm varies valve timing automatically, by increasing or widening valve lash at low speeds, improving low and torque horsepower, economy and smog pollution emissions, yet while engine speeds increase valve lash decreases, consequently lengthening valve duration and overlap improving high speed performance.